THERMAL STRUCTURE OF THE MESOPAUSE REGION AT POLAR LATITUDES

We present the results of temperature soundings performed on almost 180 days since 1980 in the 50- to 120-km altitude range at Andenes, Norway (69-degrees-N latitude). Most of the temperature profiles were obtained by ground-based lidar; the others were derived from in situ density measurements. We present (1) monthly mean temperatures for 9 months of the year, including the mesopause temperature and altitude, and examine (2) seasonal effects, (3) interannual variability, (4) systematic differences to CIRA 1986, and (5) longer-term effects related to the solar activity cycle. The main results are as follows: the mesopause is high (98 km) and warm (192 K) in a long period from October to March and low (88 km) and cold (129 K) in June and July. The transition between these two states in August is much faster than commonly anticipated. An intercomparison of our monthly mean temperature profiles with CIRA 1986 shows significant deviations. Above 80 km we find positive correlations between temperature and solar activity with regression coefficients in the order of 0.15 K/SFU.